Dynamo voltage control



Nov. 18, 1958 w. KOBER 2,861,238

DYNAMO VOLTAGE CONTROL original Filed March 27; 1951 5 Sheets-Sheet 1 ir/,,, X E a I s 1: 3 E 5 \7? 7/ 40 INVENTOR. ML LIAM K0552 n to'RAlsrs.

Nov. 18, 1958 T KOBER 2,861,238

DYNAMO VOLTAGE CONTROL Original Filed March 27, 1951 3 Sheets-Sheet 3 37GENERATOR.

i MOTOR WILL/AM KoeER BY. @aa, M, Mr QM,

.4 TTORNEYS.

United States Patent DYNAMO VOLTAGE CONTROL William Kober, Fairport, N.Y.

Original application March 27, 1951, Serial No. 217,799,

new Patent No. 2,784,332, dated March 5, 1957. Divided and thisapplication March 1, 1957, Serial No.

11 Claims. '(Cl. 32246) The object of this invention is to construct analternating current generator using a rotating permanent magnet field insuch a way that the voltage output can be varied readily, over a widerange. This application is a division of my pending application, SerialNo. 217,799, filed March 27, 1951, now Patent No. 2,784,332, dated March5, 1957.

A further object of this invention is to provide means whereby thevoltage of the generator can be varied over a large range withoutproducing any appreciable distortion of the output voltage wave form.

'A further object is to provide means whereby the voltage control isautomatically operated in a way to keep the output voltage constant withvariations in speed and load.

A further object is 'to operate the voltage control automatically torespond in a desired way to changes in output current and power.

Alternating current generatorsusing fields energized by permanentmagnets have a number of advantages over the conventional type ofgenerator, in which thefield is excited by an auxiliary current. Some ofthe more obvious are: elimination of the need for a direct currentexciting source, and of brushes and slip rings to conduct the currentinto the rotor, and reduced heating in the generator resulting from theelimination of field excitationlosses. It is also true at this time,because of the perfection of excellent permanent magnet materials, thata.;given size and weight of permanent magnet field structure willproduce more magnetomotive force and more flux than an equal size andweight of electromagnetically excited field.

It is Well known that generators ofboth types will show considerablevoltage drops under load increases, particula'rly when the generatorsare made for applications where minimum size and weights are essential.Also, generators of both types will change their voltages with changesof speed of rotation, and such changes are often considerable.

With the electromagnetic field type, it has become wellnigh universalpractice to overcome these unwanted voltage changes by controlling thefield produced through variation of the field exciting current. Theresulting regulators are well known, and need no further descriptionhere.

With generators using permanent magnet fields, this type of control isobviously not available. In fact, heretofore no satisfactory means forvarying the voltage has been available. As a result, such generatorshave normally been designed to operate on inherent regulation, with theresult that the generator either had undesirably large variations inoutput voltage over a range of load or became much larger in size andweight than would have been required to generate only the maximumavailable output. Also, the change of voltage with speed could not becorrected.

.The control of the voltage of permanent magnet field ice generators wasin fact so difiicult that even minor adjustments in original voltage, tocompensate for manufacturing variations, were made only with greatdifiiculty.

In this invention, structures of a permanent magnet field generator aredisclosed which permit a simple, mechanically rugged means ofcontrolling the output voltage over a large range, either by manual orautomatic control. The methods of the invention may also be applied togenerators using any type of excitation, as well as to the permanentmagnet type.

In constructing a generator, a number of advantages are to be found inusing a cylindrical surface on the field structure which faces acylindrical armature surface across an air gap. These advantages havedetermined the present standard construction. In such a construction, itis very difiicult to control the length of the air gap. However, theseconsiderations do not retain their importance for permanent magnet fieldconstruction. A construction in which the field produces its flux on aflat ring, facing an armature similarly shaped across an air gap, hascertain important advantages.

It has been discovered that a generator of this type can have its outputvoltage varied readily by moving the armature small distances directlytoward or away from the field. Such motions cause large percentagechanges in the air gap, since this is normally small. Since air has arelatively great resistance to the conduction of high density fluxes,relatively small changes in this distance can cause great changes in theflux reaching the armature, and in the generator voltage.

It is the purpose of this invention to disclose structures by which thearmature in such a generator can be moved in the above manner, therebycontrolling the output voltage. The motion may be applied manually, orby moving devices under the control of automatic voltage controllingcircuits. These and other advantages of the invention are described inthe following specifications and drawings. In the drawings, Figs. 1-2show a generator equipped for control of voltage according to theinvention. Pigs. 3, 4, 5 and 6 show circuits and structures forobtaining automatic voltage control. Fig. 7 shows another generatorarrangement for voltage control in accord with the invention.

In Figs. 1-2, the armature 1 is mounted on'a holding plate 39 on itsrear face (away from the field 34). In this plate, three left-hand screwthreads 4 are formed. In the housing facing the armature, threecorresponding right-hand threads 3 are formed. Three studs 40, havingleft-hand threads on one end and right-hand threads on the other arefitted into the armature holding plate and the housing. Each stud has agear 7 fastened to it, so that a fourth or driving gear 8 engages eachone, insuring equal rotation of all three studs, and equal motion of thearmature 1 with respect to the housing 5. Initial adjustment so that thestator front face is exactly parallel to the field face at all times isreadily achieved by disengaging the fourth gear initially, turning thethree stud gears individually until parallelism to the desired degree isachieved, and then engaging all the gears at the nearest meshing point.

By proper choice of pitch diameter and thread of the studs, and of gearratios, enough motion to control voltage through the useful range can beachieved by only a fractional revolution of the control gear 8 throughshaft 6. Alternatively, if desired, a considerable number of suchrevolutions may be involved. It will be noted that control can beapplied through any of the three studs, if allowed to project beyond thehousing, as well as byfthe fourth gear 8 and shaft 6.

If the central regions are to be left clear, the central or fourth gear8 may be made open internally, i. e., in

the form of a ring, in which case it is controlled in positron by thethree stud gears, and does not need a centermg shaft. This gear may alsobe an external ring, or the gears 7 may be driven by a toothed belt orby sprockets engaging a chain, all as disclosed in my copendingapplication Serial No. 217,799.

' Although three studs are a minimum efficient number, it is possible touse four, five, six or more, operated together in a similar manner.

Also, the driving devices for the studs may be on projections behind thehousing, instead of between the housing and armature, all as shown in mysaid copending application, Serial No. 217,799.

For automatic control, the control shaft may be driven by a small motorunder the control of voltage, current and power sensitive devices. Themotor may be run by D. C. as in Fig. 5, single phase A. C. as in Fig. 4,or polyphase A. C. as in Fig. 3, the latter beingpreferred, since asmall polyphase output can always be taken from the generator for thepurpose of powering the motor.

The motor may be driven in two directions, as in Figs. 3 and 5, or inone direction with a spring return, as in Fig. 4. In this latter form,the motor need not be reversible, the spring always tending to return itto the starting point.

Fig. illustrates the system employing a reversible D. C. motor. Since asingle pole double throw relay (back and front contact) is moresensitive than a double pole type, it is preferred to use a rectifierwhich has a center tap, to supply the motor, one simple form of which isshown. It is necessary to draw the motor power from a rectifierindependent of the control rectifier, to avoid disturbing this verysensitive circuit. It will be noted that the proper performance of themotor does not depend on any particular constancy of its power supply,hence no special precautions need to be taken in this rectifier circuit.

The operation of Fig. 5 is explained as follows. Suppose that afterconstant operation at a given speed and load, the speed of the generatorsuddenly increases, while the load remains constant. The voltage of thegenerator on lines A, B, C tends to increase. This increase passesthrough the transformer 29, where a voltage suitable to rectifier 39 isproduced. The use of three phase circuits to this point insures anaverage response if an unbalanced load on the generator causes somedifference in the voltage of the individual phases. However, the use ofone phase only is obviously possible. Rectifier 39 passes on theincrease to relay 20, causing spring 21 to move to the front contact.Relay 20 is designed to have a very small voltage differential betweenits front and back contacts. The front contact associated with spring 21closes the armature circuit of motor 31, causing it to rotate shaft 27(connected to the main generator shaft 27 by means not shown) in such amanner that the generator stator is moved to increase the air gap. Thismotion continues until the generator output voltage has decreased to itsdesired value, when relay 20 opens its front contact, and the springfloats free of both contacts. The generator now operates under the newspeed condition at its desired substantially constant voltage. If thespeed decreases rather than increases, the terminal voltage tends todrop, causing the voltage across relay 20 to drop, causing spring 21 tomake its back contact. Motor 31 now rotates in the opposite sense tothat described before, since its field polarity is unchanged, but itsarmature polarity is reversed. As a result, shaft 27 moves the generatorstator toward the rotor. This process continues until the voltagereturns to normal when spring 21 floats away from its back contact andthe motor stops. To prevent overrun of the motor, and consequentsurging, suflicient friction may be built into the motor or an automaticmagnetic brake may be applied in a manner known to the art.

If the voltage of the generator drops by reason of a load change oralternatively rises by reason of a load change, similar responsescorrecting the voltage take place. The same holds true for anycombination of speed, load or load power factor changes.

The function of current transformers 41 and frequency responsivenetworks 40 has not yet been described. These are useful when it idesired to over or under correct for volatge changes due to load orfrequency changes. Thus, if voltage sensitive equipment is separatedfrom the generator by a long transmission line having considerableresistance and reactance, it may be desirable to over or under correctthe voltage at the generator in such a way that the effect of thetransmission line is compensated for. The procedure in adjustment ofnetworks 40 and controls 28 requires only ordinary skill.

Fig. 3 shows a system similar to Fig. 5 except that a reversible threephase motor 22 is used to move shaft 27. To reverse the motor on motionfrom a front contact to a back contact at relay 21, Scott transformer18, which produces alternative phase rotation on the three phase motorterminals in a well known way is employed.

In Fig. 4, a simpler system suitable for a single phase generator 16 andusing a return spring 26 in combination with a single direction drivemotor is shown. Here spring 26 always tends to turn control shaft 27 ina direction to reduce voltage. Any actual reduction in terminal voltage,however, causes the back contact of relay 23 to make, driving motor 25in a direction to increase voltage. Thus, a vibration of the relaycontact is established, holding the terminal voltage exactly at thepoint of making of the contact. It is also possible to operate thissystem with the spring 26 driving to higher voltage, and the backcontact of relay 23 replaced by a front contact. However, on failure,the voltage will rise, a sometimes less favorable result than that givenby the previous system in which it drops.

When parallel operation is intended, appropriate interconnections ofregulators in the usual way will serve to keep circulating currents inthe paralleled generators at a minimum.

Fig. 6 shows a system of automatic control in which the motor isreplaced by a magnetic clutch 33 driven by the main generator shaft 35.The clutch may be of the mechanical contact type, of the iron filingstype, or preferably of a type in which the torque is produced bymagnetic drag across an air gap without any mechanical contact.Operation is analogous to that described for Fig. 4, except that themore delicate D. C. relays 20 of Figs. 3 and S, and their associatedcircuits will be preferred.

In the clutch system shown in Fig. 6, it is possible to make the clutchquite sensitive, and sharply responsive in torque to small variations ininput voltage. The intermediate relay of Figs. 3, 4 and 5 can then bedispensed with, and the clutch be energized directly by the controlvoltage, made up in part of voltage, and in part of current and relativephase as in Fig. 5. The voltage supply to clutch 33 now is that going torelay 20 in Fig. 3 or 5. The networks 40 and the adjustments 28 now takeon a new function. To secure operation, the springs must drive to highervoltage because the clutch, energized by the control circuit, pullsharder at higher voltage and this harder pull must be directed tocorrect its cause or to reduce voltage. Thus, at peak loads, the springswill be at their loosest point and less control voltage will be calledfor causing a reduced terminal voltage. Here then, this system onlyreduces the effect of load and speed changes but does not neutralizethem. However, exact neutralization or even overcorrection may beobtained by use of networks 40, transformers 41 and adjustments 28. Thecurrent adjustment 41 and 28 is set to oppose the line voltage tappedfrom A, B and C. Thus, at high currents, but constant line voltage, thecontrol voltage applied to clutch 33 is reduced. If this reduction isadjusted to the right value, constant voltage at all loads is obtained.By interchanging phases between the current and voltage taps, a similareffect due to changes in load power factor can be neutralized. Thefrequency responsive networks 40 may be similarly adjusted so that alower frequency produces an accentuated voltage drop, thus neutralizingthe eifect of the full range of speeds on voltage. Thus, all effects ofchanging conditions may be neutralized, giving constant voltage outputat the generator terminals under all conditions. This system dispenseswith all make and break contacts in the entire generator and controlsystem.

It is often preferred to place the clutch and drive gears in an enclosedlubricated space, leaving the back of the stator free for coolingaction. This general plan, shown in Fig. 6 of my pending application,Serial No. 217,799, is obviously adaptable to the clutch system of Fig.6.

In the above forms, the use of left-hand and right-hand screw threadshas been shown to secure parallel motion of the stator. Single threadsand a collar may also be used. Additionally, any other parallel motiondevice, actuated by wedges, cams or levers is available to produce thedesired motion when desired.

The relative motion between the stator and the field may also beobtained by moving the field and fastening the statorin fixed relationto the housing. In Fig. 7, the stator 1 is so fastened and rotor 34 ismoved toward and away from it by moving bearing 43 on shaft 45 in itsouter housing by moving shoulder 42. The motion may be imparted by ascrew 44 or by other obvious means. It will be noted that the magneticattraction between rotor and stator produces an axial force which holdsthe bearing against shoulder 42. Therefore, the opposing shoulder 47 canbe eliminated if desired.

I claim:

1. In a dynamoelectric generator, an armature, a rotating field, saidarmature and said field having parallel working faces spaced apart alongthe axis of rotation of said field to provide an axial air gaptherebetween, said field producing magnetic flux entering said armatureacross said air gap, means mounting at least one of said armature andsaid field for movement relative to the other thereof in the directionof said axis of rotation whereby to change the length of said air gap,said means including position adjusting means operable to so move saidone of said armature and said field while at all times maintaining theparallel relation between said working faces, and actuating means forsaid position adjusting means controlled by the output of said generatorfor actuating said position adjusting means automatically to maintain asubstantially constant generator output.

2. In combination, a dynamoelectric generator having a stator, a rotormounted for rotation about a predetermined axis, said stator and saidrotor having parallel working surfaces spaced apart in the direction ofsaid axis of rotor rotation to provide an axial air gap therebetween,means mounting at least one of said stator and said rotor for movementtoward and away from the other thereof in the direction of said axiswhereby to vary the length of said air gap, and means for so moving saidone of said stator and said rotor automatically in response tovariations in an output characteristic of said generator, saidlast-named means including a motor, an energizing circuit for saidmotor, and a control circuit for said energizing circuit operableindependently thereof in response to such variations to causeenergization of said motor to so move said one of said stator and saidrotor ina direction to produce a desired generator outputcharacteristic.

3. The combination set forth in claim 2, wherein said motor energizingcircuit draws power from the output of said generator.

4. The combination set forth in claim 2, wherein said motor comprisesa-reversible D. C. motor having constant field polarity, said controlcircuit being operable to cause said energizing circuit to reverse thearmature polarity of said motor.

5. The combination set forth in claim 2, wherein said prises areversible polyphase A. C. motor, and said energizing circuit drawspower from the output of said generator, said control circuit beingoperable to cause alternative phase rotation in said motor energizingcircuit.

6. The combination set forth in claim 2, wherein said control circuitcauses energization of said motor in one direction only, and said motorhas a spring return.

7. The combination set forth in claim 2, wherein said generator has anA. C. output, and said control circuit includes a D. C. relay incontrolling relation to said energizing circuit, and means includingrectifier means for energizing said relay in response to variations inthe generator output.

8. In combination, a dynamoelectric generator having a stator, a rotor,means including a shaft mounting said rotor for rotation about apredetermined axis, said stator and said rotor having parallel workingsurfaces spaced apart along said axis to provide an axial air gaptherebetween, means mounting at least one of said stator and said rotorfor movement toward and away from the other thereof along said axis tovary the length of said air gap, and means for so moving said one ofsaid stator and said rotor automatically in response to variations in anoutput characteristic of said generator in a direction to produce adesired generator characteristic, said lastnamed means includingcoupling means for operatively connecting said mounting means to saidshaft for being driven thereby to so move said one of said stator andsaid rotor, and energizing circuit means for said coupling meansresponsive to the output of said generator.

9. The combination set forth in claim 8, wherein said coupling meanscomprises a clutch having working surfaces spaced apart by an air gap,one of said surfaces being driven by said shaft, and said energizingcircuit means is operable to produce a variable magnetic force couplingsaid clutch surfaces across said last-named air gap.

10. The combination set forth in claim 1, wherein said actuating meansare controlled by means including means responsive to the output voltageand the output current of said generator.

11. The combination set forth in claim 10, wherein said meanscontrolling said actuating means also include means responsive to theoutput frequency of said generator.

References Cited in the file of this patent UNITED STATES PATENTS614,608 Cantono Nov. 22, 1898

